The invention relates to a laser light barrier system for measuring or checking tools or workpieces on machine tools. It includes a support housing which can be fastened to the machine frame and comprises an elongate base housing and two block housings, which at a mutual longitudinal distance project transversely from the base housing and one of which contains a transmitter and the other a receiver, the laser beam extending at a distance from and approximately parallel to the base housing. The laser beam may also have the form of a narrow ray bundle which is focused on the center of the beam path and then diverges. In this case, the axis of the ray bundle follows the same course as the abovementioned laser beam. Systems of this kind are used, for example, for setting rotating tools, for checking for tool breakage, for measuring the trajectory diameter of rapidly rotating tools and for length measurement, in particular for compensating for the thermal expansion of the measuring arbor.
Since all the important functioning parts are mounted on a common support, the system forms a structural unit which is ready for connection and can be used as an accessory to machines from a very wide variety of manufacturers and designs.
An important practical requirement of such a structural unit consists in protecting the sensitive transmitter and receiver components against the coolant spraying around in the machining space of a metal-working machine and against other environmental influences, but nevertheless allowing the laser beam an unimpeded opening for entry and exit. In the case of known systems, this is accomplished using blocking air and by means of mechanical closures for the opening.
The signal which is generated if the laser beam is interrupted usually acts directly on the NC system of the machine by stopping the feed as soon as the tool interrupts the laser beam. The reliability of this operating circuit is of particular importance, since otherwise there is a risk of damage to the machine and possibly of injury to the operator. However, since on the other hand, as mentioned, these systems are accessories not built in the factory, experience has shown that faults cannot be ruled out during adapting to the machine's own control system. The faults may arise on the laser light barrier system itself, in the signal processing (owing to computer errors) or as a result of incorrect programming, and therefore still constitute a considerable risk factor.